Inconel 718: known as high‑nickel alloy steel
19 Aug,2026
Inconel 718 is a precipitation‑hardening alloy featuring high Ni, high Cr and high Nb. With nickel content up to 55 %, it is also referred to as high‑nickel alloy steel. It delivers high strength and good toughness at temperatures up to 700 °C, alongside corrosion resistance under both high‑ and low‑temperature conditions.
It is supplied in either solution‑treated or precipitation‑hardened condition. Thanks to its high‑temperature strength, outstanding corrosion resistance and good machinability at 700 °C, Inconel 718 is widely used in demanding applications, such as steam turbines, liquid‑fuel rockets, cryogenic engineering, acidic service environments and nuclear engineering. In the materials industry, it is mainly manufactured into strips, bolts, nuts, forgings and other components.
## 1. Definition and Chemical Composition
Inconel 718 is a nickel‑base superalloy. Its main chemical constituents include nickel (Ni), chromium (Cr), iron (Fe), niobium (Nb), molybdenum (Mo), titanium (Ti), etc.
- Nickel: approx. 50‑55 %. As the matrix element, nickel provides good corrosion and oxidation resistance, and maintains favorable toughness and strength at elevated temperatures.
- Chromium: 17‑21 %. Chromium improves high‑temperature oxidation resistance by forming a stable chromium‑oxide protective film on the alloy surface to prevent further oxidative attack.
- Iron: approx. 18‑20 %. Iron partly affects material cost and certain properties.
- Niobium: 4.75‑5.5 %. Together with titanium, niobium forms strengthening phases with nickel, greatly boosting alloy strength via the age‑hardening mechanism.
- Molybdenum: 2.8‑3.3 %. Molybdenum enhances creep resistance and corrosion resistance.
## 2. Performance Characteristics
### High‑temperature Properties
Inconel 718 exhibits excellent performance at high temperatures with superior creep resistance. Creep means slow plastic deformation of materials under constant stress at high temperature. For high‑temperature components such as aero‑engine parts, Inconel 718 maintains dimensional stability over long‑term high‑temperature and high‑stress service and avoids component failure caused by creep. Its creep resistance meets stringent engineering requirements even at 650‑700 °C.
It also possesses remarkable high‑temperature strength. Tensile strength and yield strength decrease slowly under heat, attributed to its complex alloy‑strengthening mechanisms. After aging treatment, internal γ'' and γ′ strengthening phases effectively resist high‑temperature deformation, enabling the alloy to sustain heavy mechanical loads for components like gas‑turbine blades and hot‑section parts of aero‑engines.
### Corrosion Resistance
Inconel 718 resists various corrosive media. In oxidizing environments, the surface chromium‑oxide film effectively mitigates high‑temperature oxidation. It performs well in aggressive chemical media including seawater, acidic and alkaline solutions. In marine environments, it resists flow‑accelerated seawater corrosion as well as chloride‑induced pitting and crevice corrosion. For chemical‑process services involving media such as sulfuric acid and hydrochloric acid, Inconel 718 shows favorable corrosion resistance within appropriate temperature and concentration ranges.
### Machinability
Hot working of Inconel 718 is relatively challenging. High alloying‑element content makes the material prone to hot cracking during hot processing. Nevertheless, hot operations such as forging and hot rolling can be accomplished with properly controlled process parameters including forging temperature and deformation rate; the typical forging temperature range is 950‑1050 °C.
Cold working also presents difficulties. The alloy suffers significant work‑hardening during cold forming. Its high strength and hardness cause heavy tool wear. Intermediate annealing can relieve work‑hardening and facilitate cold processing. For instance, timely annealing during cold rolling restores ductility for subsequent forming operations.
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